Targeted Acquisition Of Fusarium Oxysporum F.sp.niveum Toxin-deficient Strains And It With The Inactivated Mycelium's Effect On Overcoming Continuous Cropping Obstacle Of Watermelon

Watermelon fusarium wilt is a common soil-borne disease in watermelon cultivation caused by the infection of Fusarium oxysporum f.sp.niveum(FON),which has become a major limiting factor for watermelon production.Fusaric acid is a non-specific toxin produced by all fusarium species,which is a major toxin secreted by Fusarium oxysporum f.sp.niveum(FON).In this study,we intended to obtain pathogenic factor(toxin)-deficient endophytic strains on the basis of wild bacteria for biocontrol from the perspective of not changing the niche and host specificity of pathogen.The pot experiment showed that deficient-strain had a certain role in mitigation continuous cropping obstacles of watermelon,which provides a new idea and method to overcome barriers of continuous watermelon.In this study,we designed primers for the homologous conserved region by selecting the FUBT gene involved in toxin transport in the Fusarium oxysporum to obtain the upstream and downstream sequences of the target gene.Fusion PCR was performed using hygromycin as the screening marker,and finally toxin-deficient strains were obtained by homologous recombination.We used the targetedly obtained toxin-deficient strain(FO-1)as the biocontrol strain to control the watermelon fusarium wilt.The growth and sporulation of ?FUBT were examined,and no significant differences were found from the wild strain(data shown).The inoculation results of FO-1 revealed that it could still infect and colonize watermelon.Toxin production test showed that a decrease in toxin production by 26.5 ?g/mL in FO-I(112.3 ?g/ml for the wild strain).The applied deficient strain increased total yield by 8.3%,the microbial population in the soil changed to some extent,the amounts of bacteria and actinomycetes increased significantly,while the amount of fungi decreased compared to the control.The bacterial amount increased by 34.1%,23.0%and 30.6%,respectively;compared to the control at the flowering stage,fruit setting stage and maturation stage.At the maturation stage,the amount of actinomycetes increased by 39%compared to the control,while the amount of fungi decreased by 24.6%.The FO-1 amount in the soil also presented a dynamic change,which was up to 2.2×103/g at the fruit setting stage.Accordingly,the amount of FON at the fruit setting stage decreased by 16.8%.After administration of deficient strain,the root vigor of watermelon increased significantly,which remained a stable level till the maturation stage.Compared to the control,the root vigor increased by 29.65%,7.5%and 10%,respectively,at three different stages.Compared to the CK treatment group.The underground CAT activity increased significantly by 5.6%in the H treatment group;shoot SOD activity increased significantly by 6.2%;shoot and root POD activities increased by 4%and 7.3%;and the shoot MDA activity decreased significantly by 14.6%.The soil urease activity in H-treatment group was 111.0%,15.2%and 57.1%higher than that in the CK group at flowering,fruit setting and maturation stages,and soil sucrase activity increased by 51.8%,36.3%and 21.3%,respectively.Compared to CK,polyphenol oxidase activity increased by 32.5%,76.2%and 31.9%in the H treatment group,respectively,at the flowering,fruit setting and maturation stages.At the flowering and fruit setting stages,soil catalase activity increased by 29.8%and 7.7%,respectively.The activity of soil alkaline phosphatase in the treatment group differed significantly from the CK treatment group only at the fruit setting stage,which was 8.6%higher than the CK treatment group.The treatment of deficient strains balanced the structure of soil microbial community,improved soil microenvironment,induced a systemic resistance of watermelons to the invasion of FON,and can alleviate the continuous cropping obstacles of watermelon.In order to induce the antagonism and prey on fusarium oxysporum microorganism enrichment in the soil,FON mycelia was inactivated processing,and than throw in continuous cropping watermelon rhizosphere.Compared to the CK treatment group.The inactivated mycelia increased total yield by 8.3%,disease index decreased by 166.7%.Inactivated the mycelium of improved soil microbial quantity,compared to CK treatment group,in the amount of bacteria and actinomycetes of mature period decreased significantly by 150.0%and 100.13%respectively in inactivated mycelia treatment,as the same time the amount of fungi decreased by 150.48%.The amount of FON in the soil was also significantly suppressed,decreasing by 52.34%and 61.97%respectively during the period of fruit and maturity.Compared to CK treatment group.The shoot and root CAT activity increased significantly by 18.94%and 48.05%,respectively.The shoot and root MDA activity was reduced significantly by 66.67%and 78.46%,respectively.The shoot and root SOD activity was increased significantly by 102.45%and 38.99%respectively.The shoot and root POD activity were increased significantly by 55.46%and 40.90%.The inactivated mycelium inhibited the number of FON,promoted soil microbial diversity,improved soil microenvironment,and improved watermelon resistance enzyme and root energy.We speculate that the inactivated hyphae imposed by influencing soil microfauna predation,attract specific enrichment of microorganism,induced resistance of watermelon way relieve watermelon continuous cropping obstacle.